A practice that began in sunshine and ended indoors to escape the rain had finished minutes earlier. Will Beatty was now alone in the weight room, lying on his back and doing crunches at a maddening pace.

The extra work was a good sign, considering this time last year Beatty was lost for the preseason due to back problems. Being healthy is just one reason the Giants starting left tackle practically is bouncing on his toes during training camp. The light bulb has gone on. He’s ready to be a pro’s pro.

“I’m having more fun now even though I’m older,” the 28-year-old Beatty said. “When I was younger I was healthier and more athletic. But the more you know about this game, the more you understand it, the easier and faster you can play.”

Beatty is the youngest

member

of the Giants offensive line expected to start the season against the Cowboys. Left guard Kevin Boothe is 30, center David Baas and right guard Chris Snee are 31, and right tackle David Diehl is 32. They are among the most seasoned in the NFL — a strength of the Giants’ offense and blessing to a defense that has to work against them every day.

“They know all the tricks of the trade, and they’re constantly trying to use it against us,” defensive end Justin Tuck said yesterday. “That’s just going to help us even more. You know you’re going to get great looks all week. If we can hold our own against them, we’ll have a great shot of doing it against the offensive lines we play on Sundays.”

Beatty has to prove he can hold his own. The Giants signed him to a five-year $38.7 million contract to protect Eli Manning’s back side. The Giants can’t afford for Beatty to fail or be injury prone.

Despite starting 31 games through his career and earning a rich contract, the 2009 second-round pick from UConn still is trying to develop a higher level of nastiness and consistency. He won’t ever be Jumbo Elliott. But at 6-foot-6, 319 pounds, Beatty has the body to impose his will, and the Giants need him to do just that.

“He’s in his fifth year and he’s grown each year,” Boothe said. “It’s not hard to see his development as a player both on the field and off the field in terms of his knowledge of the offense.”

Beatty yesterday looked like a young colt ready to be unleashed. He said he was eager for tomorrow’s preseason opener against in Pittsburgh because, “You get to be a bull … you get to run around and hit people and it’s all legal.”

He also is comfortable with his knowledge of the offense and the expectations of his coaches and QB.

“Preseason is a wonderful chance for you to work on your technique to try new things out … to bond with the guys you’re working with,” Beatty said. “We have a mature offensive line that knows Eli very well. You know he sees the same thing you see.”

It’s crucial to the Giants’ present and future Beatty stabilizes the left tackle spot. Brandon Mosley, a fourth-round draft pick in 2012, will start tomorrow night at right guard for Snee, and figures to be part of the Giants’ long-term plans, as does Justin Pugh, the 2013 first-round choice from Syracuse, who is out temporarily with a concussion. Pugh is the projected replacement for Diehl.

Beatty is part of that long-term future, too. But the Giants need him to be a little nastier and more consistent now.